Abstract 4498: Lysyl oxidase like-2 mediates tumor to stromal cell communication in oral cancer

Abstract

Abstract Introduction: The lysyl oxidase family consists of 5 members and oxidizes specific lysine residues in biosynthetic collagen and elastin maturation. Lysyl oxidase like-2 (LOXL2) is elevated in oral cancer and promotes metastasis and correlates with poor prognosis. The objective of this study is to determine the mechanism by which LOXL2 promotes the progression and invasiveness of oral squamous cell carcinoma. Methods: In vitro: To investigate functions of LOXL2 in oral cancer, the effects of LOXL2 inhibitor (PXS-S1C) on human gingival fibroblasts treated with tumor cell conditioned medium (CM) were investigated. Cell proliferation assays, signaling arrays and western blots were used to evaluate the effect of PXS-S1C on CM-treated fibroblasts. The effect of PXS-S1C on cancer cells expression of LOXL2 and proliferation was determined. To find potential LOXL2 substrates in gingival fibroblasts treated with CM +/- PXS-S1C, carbonyl-containing proteins were purified by affinity chromatography and identified by MS and western blot. In vivo: The effect of PXS-S1C on cancer growth and metastasis in vivo was investigated using an orthotopic oral tongue cancer mouse model in both immunodeficient and immunocompetent mice. PXS-S1C at 10 mg/kg and 30 mg/kg was injected immediately following tumor cell injections. Tumors were monitored by caliper measurements, and by in vivo imaging (IVIS). The mice were sacrificed and their organs were subjected to immunohistochemistry staining for proliferation markers. Results: PXS-S1C significantly inhibited gingival fibroblast proliferation triggered by tumor cell CM and attenuated phosphorylation of PDGFRβ Y771 and P-PDGFRβ Y857, but not PDGFRβ Y751 in response to CM. PXS-S1C inhibited ERK1/2-signaling in fibroblasts and not AKT in response to CM. PDGFR activation by oral tumor cells was mimicked by PDGF-AB, but not PDGF-BB. PXS-S1C decreased the expression of LOXL2 by 5-fold in HSC3 oral cancer cells in vitro, suggesting a positive autoregulatory loop. Assessing for direct LOXL2 substrates in fibroblasts with functional consequences identified both PDGFR and integrin αV. Caliper measurements, IVIS, and immunohistochemistry demonstrated that inhibition of LOXL2 significantly decreases oral cancer progression and metastasis in vivo. Mice without PXS-S1C treatment developed larger tongue volumes (p<0.05), and more mice developed larger lymph nodes (3 out 12) compared to the PXS-S1C-treated mice (1 out of 12). IVIS imaging revealed inhibition of metastasis by PXS-S1C treatment. The expression of proliferation marker (Ki-67) and LOXL2 was lower in tongue tumors treated with PXS-S1C (p<0.05). Conclusions: LOXL2 secreted by cancer cells stimulates fibroblasts by enhancing PDGFR signaling and proliferation, and by stimulating αV integrin function and cell adhesion. Inhibition of LOXL2 could provide therapeutic strategies to address oral cancer. Citation Format: Faranak Mahjour, Philip C. Trackman. Lysyl oxidase like-2 mediates tumor to stromal cell communication in oral cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4498.